Heat-sensitive copying sheets



A. E. BOLLINGER ETAL 3,180,752

HEAT-SENSITIVE COPYING SHEETS Filed NOV. 6, 1961 A ril 21, 1965 DP}! QUEBil/SHED C04 TING CONTAIN/N6 METHYL METIMCRYLATE POL YMER BACK/N6 SHEETUnited States Patent 3,180,752 HEAT-SENSITIVE CORYING SHEETS Albert E.Bollinger, Silverton, Ohio, Jerome M. Delaney,

Covington, Ky., and John F. McHugh, Brookiyn, N.Y.,

assignors to Interchemical Corporation, New York,

N.Y., a corporation of Ohio Filed Nov. 6, 1961, Ser. No. 150,180 5Claims. (Ci. 117-36.7)

This application is a continuation-in-part of our application S.N.841,673, filed September 23, 1959 (now abandoned). This inventionrelates to heat-sensitive copying paper useful in preparing copies ofprinted matter or other graphic originals.

Heat-sensitive copying papers are old in the art. In fact, there are atleast two distinct types of such paper. One operates by means of a heatactivated chemical change that occurs in the paper, or in the coating onthe paper. Another type operates by means of a physical change that isproduced by heat. The present invention relates specifically to the typeof heat-sensitive copy paper wherein the image on the copy sheet isproduced by a physical change in the coating.

US. Patent No. 2,710,263 and Reissue Patent No. 24,554 describedheat-sensitive coatings for making copying paper in which the imageappearing on the copy sheet results from a physical change in thecoating corresponding to the image copied. According to the teachings ofthese prior art patents a heat-sensitive copying paper can be preparedby coating a dark colored supporting base with a composition consistingof particles of a normally transparent stable organic fusible solid,melting within the range of 60-115 C., dispersed in a solution of atransparent film-forming binder in a volatile solvent, evaporating thesolvent without fusing or dissolving the particles so as to provide anon-transparent, infrared transmitting, heat-sensitive layer. Aprotective layer of film forming material can be applied over theheat-sensitive layer if desired. Heating the sheet at temperatur'escorresponding to the melting point of the fusi- 1..

ble solid melts the heat-sensitive coating and allows the dark coloredbase sheet to show through at the heated areas. In making copies ofgraphic originals the heated areas would correspond to the image on theoriginal and would result, from heat generated by exposing the originalto high intensity infrared radiation. Preferably the copy is made byplacing the copy sheet on the original with its uncoated side next tothe original and then exposing the original through the hcat-sensitivecopy sheet. In an alternate technique the original would be exposed toinfrared radiation directly with the coated side of the heat-sensitivepaper immediately back of it. By this back-printing technique it is notnecessary, of course, that the heat-sensitive paper be infrared,transparent. Both the back-printing and the front-printing techniquesare'described in the prior art patents mentioned above and also in US.Patent No. 2,859,351.

The art also teaches how to make heat and pressuresensitive sheet, orpaper, e.g., to be used with recording instruments having heated styli.The coating on these papers, like that of the US. patents referred toabove,

which may or may not be plasticized with solvent type plasticizers. Theheat-sensitive papers of this type that are known to the art are notheat-sensitive enough to have any practical use in the thermocopyingprocess of US. Patent No. 2,859,351. For instance, when they areemployed in the method of US. Patent No. 2,859,351 for making copiesthey give only faint copies or no copies at all.

Heat and pressure-sensitive papers that are designed for use 'withheated styli, and which comprise discontinuare discontinuous films ofthe film forming materials ous film-forming resin coatings on a darkcolored base sheet are prepared either by the bushing lacquer technique(US. Patent No. 2,519,660) or by coating with a water-in-lacqueremulsion (US. Patent No. 2,739,909) wherein the solvent of the lacqueris more volatile than water. The film-forming resin may be a celluloseether or ester, polymethyl methacrylate, polystyrene,vinylchloride-vinyl acetate copolymers, and coumarone-indene resins.Addition of solvent type plasticizers to these coatings improves theheat-sensitivity but it also softens the coatings to the extent thatthey are not sufficiently abrasion resistant for ordinary handling inmaking copies and in filing, mailing, etc.

It has now been discovered that very desirable heatsensitive papers foruse in the process of Patent No. 2,859,351 can be produced by theblushed lacquer technique provided certain specific limitations are met.The limitations are: (1) the film-forming material must be thermoplasticmaterial which melts above about C., and (2) the film must contain aminor amount of a liquid or low melting, substantially non-volatilenonsolvent type plasticizer, or lubricant.

In accordance with the invention there is provided a heat-sensitivecopying sheet composed of a non-metallic supporting base and anon-transparent, heat-sensitive, blushed lacquer coating thereoncontaining a major amount of a solid thermoplastic polymer and a minoramount of non-solvent, lubricant type plasticizer. The stability of thecoating during storage is largely governed by the melting point of thethermoplastic filmforming polymer; for this reason a polymer having ahigh melting point is desirable. On the otherhand, the polymer, or atleast the polymer plus the secondary plasticizer, must be heat-sensitiveat a reasonable temperature, i.e., the coating must transparentize at atemperature that is readily obtainable and is not high enough to damagethe base sheet.

Polymethyl methacrylate polymers having a melting point above 125 C. anda molecular weight above 300,000 (as determined by intrinsic viscositymeasurements) have been found to be ideally suited as the majorfilm-forming material of the blushed film. A typical polymer that iscommercially available is Lucite 41 having a melting point of about C.and a molecular weight of 334,000 as determined by intrinsic viscositymeasurements.

For overall properties butyl stearate has been found to give the bestproduct of any of the non-solvent type plasticizers tested. As the nameindicates, the non-solvent plasticizer, or lubricant type plasticizer,is substanstantially incompatible with the polymer, at least at roomtemperature. The lower limit of non-solvent plasticizer content is notparticularly critical and is governed largely by the temperature atwhich the heat-sensitive paper is to be used. Using commerciallyavailable equipment, such as the Thermo-Fax Copying Machine (fromMinnesota Mining and Manufacturing Co.) a blushed film containing 20parts butyl stearate to 80 parts Lucite 41 has been found to be verydesirable. Lower ratios can, of course, be used, especially when thepaper is to be used at higher development temperatures. Higher ratios ofbutyl stearate can be used but are less desirable especially when goodabrasion resistance is needed. By experience it has been noted thatratios higher than about 45% non-solvent plasticizer are notsufficiently abrasion resistant to be of any practical use in theThermo-Fax Copying Machine.

The blushed film may contain small amounts of certain flatting agents todecrease the gloss of coating. We have found, for instance, that smallamounts of metal soaps The blushed films are formed on the paper bycoating with a blushing lacquer containing the thermoplastic polymer andbutyl stearate, or equivalent non-solvent plasticizer, dissolved in amixture of at least two volatile organic liquids, the more volatile ofwhich is a solvent for the thermoplastic polymer and the other is anon-solvent for the polymer. When applied to the paper the two "solventsare present in such a ratio that the polymer is in solution; however, asthe more volatile solvent evaporates from the film faster than thenon-solvent, the polymer tends to precipitate to form the blushed filmthat is required. As indicated hereinabove such technique for formingblushed lacquer films is known.

With polymethyl methacrylate as the thermoplastic film- 'formingpolymer, a low boiling ketone, such as methyl ethyl ketone is apreferred volatile solvent for the polymer and a hydrocarbon fractionrich in aliphatics is the preferred non-solvent. Preferably thenon-solvent should require at least five times as long to evaporateasthe ketone solvent. 7 g

The preferred method of using the heat-sensitive copying paper of thepresent invention is by the front-printing method, i.e., theheat-sensitive paper is placed on top of the original to be copied andthe original is ex posed by passing infrared energy through the copysheet. It follows therefore that in this preferred embodiment the copysheet must be infrared transparent while at the same time it issubstantially opaque to visible light.

Heat-sensitive papers made in accordance with the present invention havemany advantages over commercially available heat-sensitive copyingpaper, the copies are more permanent when exposed to sunlight, the paperis not brittleand therefore has no tendency to crack or rupture When thepaper is folded, the paper has no tendency to curl, the paper has notendency to stick to the original during development of the color.

The following examples in which parts are by weight will furtherillustrate the invention:

The drawing shows a cross section of the copying sheet.

Example 1 A blushing lacquer consisting of 66.7 parts methyl ethylketone, 10.2 parts Lucite 41, 20.5 parts Mineral Spirits (Varnolene,boiling range 310-3 85 F.; KB 37.5), 2.6 parts butyl stearate wasuniformly coated on a black carbonizing tissue that is infraredtransparent at the rate of about 1.0 lb. of solids per 1000 sq. ft. Thecoating can be applied by conventional means, e.g., using a Mayer Rodcoater. The opaque blushed film is developed by allowing the solvents toevaporate. The heat-sensitive papers produced can be used to producecopies by the front or back printing technique using the middle exposurerange of the Thermo-Fax copying machine. If the butyl stearateconcentration in the blushed film is increased less exposure is requiredto obtain copies which would indicate that the melting point of thecomposition is decreased. However, capillary tube melting points run onthe finely divided coating indicate that as butyl stearate increases sodoes the temperature at which the coating becomes translucent} Thisindicates that factors other than the melting of the coating contributeto the success ful application of the coated paper as a heat-sensitivecopying paper. Wehave further noted that in actual performance in theThermo-Fax machine, a coating which melts at 122 C. containing 67%Lucite 41 develops ample include oleic acid, paraflin oil, propyleneglycol monoricinoleate and castor oil. 9

ing Machine.

. printing processes.

4 Example 2 A blushing lacquer consisting of 9.3 parts Lucite 41, 69.8parts acetone, 18.6 parts mineral spirits (boiling range 247-290 F.; KB33.8) and 2.3 parts butyl stearate was coated on black carbonizingtissue as in Example 1 to obtain an opaque white coated heat-sensitivepaper that can be used to produce copies by the front or back printingtechnique described hereinabove.

The blushing lacquers of either Example 1 or 2 can be coated on bothsides of the sheet. The double coated heat-sensitive sheets obtained inthis manner are useful in the back-printing technique to produce copieson both sides of the sheet. The heat-sensitive coatings on the two sidesof the sheet can be the same color or of different color as desired.

Advantageously in the practice of the present invention we can use abase paper stock that has been coated on the back side with anon-heat-sensitive resinous coating or pigmented resinous coating. Wherethe paper'isto be used by the front printing technique it is of coursenecessary that the back coating on the paper he infrared transparent.Back coating of the paper provides a means of obtaining any desirablecolor on the back. A suitable infrared transparent back coating consistsof:

Mayer Coater using a #0 rod to insure the laying down of a minimumquantity of coating.

Example 3.

A blushing lacquer consisting of 67.7 parts methyl ethyl ketone, 9.4parts Lucite 41, 19.9 parts Mineral Spirits (boilingrrange SID-340 F.;Kauri-ButanolValue V 34),,2.5 parts butyl stearate and 0.5 part zincstearate was applied at the rate of 2 to 2.5 mg. per square inch to 8#Black Fenmore paper (Schweitzer Paper Co.) in conventional manner usinga Mayer Coater. The heatsensitive coated paper obtained can be used inthe front or back-printing technique with the Thermo-Fax Copy- The paperis less glossy than the heatsensitive coated papers of Examples 1 and 2.

It is to be understood that the colored base sheet may consist of alayer or coating of a selected color coated upon a supporting base.Where such a base is used, the colored layer will be intermediate thesupporting base and the heat-sensitive coating and consequently willshow through at the heated areas. Such coated base sheets may beusedboth in the front-printing and 'back- Of course in sheets used in thefront-printing process, it is necessary that the colored layer as wellas the supporting base be infrared transparent. s

It has been found that a very desirable base sheet may be prepared bycoating a supporting base with a composition comprising a DianisidineBlue pigment Color lndex (Second Edition) No. 21185 in a vehicle comprising a polymeric binder, a volatile organic solvent for said binder and aplasticizer.-

I Example 4 A coating having the following composition:

' d Parts Pigment consisting of Dianisidine Blue C.I. No. 21185, 1 2%Medium Chrome Yellow and 12% Red Lake .C c 4.2 Cellulose acetate binderhaving a 39.8%. acetyl content -4 8.5

Acetone l 82.0 Sucroseacetate isobutyrate 5.3

was coated upon a white tissue in the conventional manner with a MayerCoater using a #0 rod so that a coating of less than 2 mg. per sq. inchwas applied. The coating was then dried at 120 F. for about 1 minute toevaporate the acetone solvent. The resulting coating was opaque anddark. A blushing lacquer coating was then applied to the colored surfacein accordance with the procedure set forth in Example 1. It should beunderstood that other polymeric binders, for example, methylmethacrylate may be used. The organic solvent selected is suitably asolvent for the binder. Other plasticizers, e.g., tricresyl phosphatemay be used.

While the present invention has been primarily described as using opaquebase sheets, particularly dark coated base sheets, it should beunderstood that the invention is not limited to such base sheets. Inaccordance with another aspect of this invention, the base sheet uponwhich the blushed lacquer films are coated may be transparent. When thiscopying sheet is used in the making of copies in the commerciallyavailable Thermo-Fax Copying Machine, the image or graphicrepresentations of the original will appear as transparent areas againsta visibly opaque background. In other words what results is a negativeimage not unlike that of a photographic negative. Copies of this typemay be projected upon a surface such as a screen using a suitableprojection device, e.g., overhead projection.

The transparent base sheet is preferably of a material which is highlytransparent. Best results have been achieved using sheets of transparentpolyethylene terephthalate, although transparent sheets of othermaterials such as cellophane, cellulose acetate, polyethylene,polypropylene and Celluloid may be used.

A highly desirable coated sheet having a transparent base may beobtained by coating the blushing lacquer composition set forth inExample 1 on a base made of a transparent sheet, 2 mils in thickness ofpolyethylene terephthalate resin marketed by E. I. du Pont de Nemours &Co., Inc. under the trademark Mylar.

Although the invention has been described with particular reference towhite, visibly opaque coatings on black paper, it is obvious that othercontrasting color combinations can be employed.

We claim:

1. A heat-sensitive copying sheet comprising an infrared transmittingnon-metallic supporting base and a visibly opaque, infrared transparentblushed coating thereon of contrasting color which transparentises whenheated, said coating comprising a major amount of a solid thermoplasticpolymer of methyl methacrylate having a melting point above C. and aminor amount of butyl stearate.

2. A heat-sensitive copying sheet according to claim 1 wherein saidsupporting base is transparent.

3. A heat-sensitive copying sheet comprising an infrared-transmittingcellulosic sheet backing and infrared transmitting heat-sensitiveblushed coating of contrasting color thereon, said coating comprising amajor amount of a solid thermoplastic polymer of methyl methacrylatehaving a melting point above 125 C. and a minor amount of butylstearate.

4. A heat-sensitive copying sheet comprising a supporting basecomprising a non-metallic sheet having coated thereon a coating having aselected color and a visibly opaque, heat-sensitive blushed coating onsaid colored coating of contrasting color to said colored coating, saidheat-sensitive coating comprising a major amount of a solidthermoplastic polymer of methyl methacrylate and a minor amount of butylstearate.

5. A heat-sensitive copying sheet according to claim 4 wherein saidcolored coating is pigmented by Dianisidine Blue pigment.

References Cited by the Examiner UNITED STATES PATENTS 2,299,991 10/42Kallock ll736.7 2,519,660 8/50 James 11736.7 2,665,262 1/54 Rolle et a1.117-36.7 2,739,909 3/56 Rosenthal 11736.7 2,962,382 11/60 Ives 11736.73,020,172 2/ 62. Mohnhaupt 117--36.7 3,057,999 10/62 Newman et al.l17-36.7

OTHER REFERENCES Modern Plastics, Encyclopedia Issue for 1961, September1960, pages 414 and 415.

RICHARD D. NEVIUS, Primary Examiner.

MURRAY KATZ, Examiner.

1. A HEAT-SENSITIVE COPYING SHEET COMPRISING AN INFRARED TRANSMITTINGNON-METALLIC SUPPORTING BASE AND A VISIBLY OPAQUE, INFRARED TRANSPARENTBLUSHED COATING THEREON OF CONTRASTING COLOR WHICH TRANSPARENTISES WHENHEATED, SAID COATING COMPRISING A MAJOR AMOUNT OF A SOLID THERMOPLASTICPOLYMER OF METHYL METHACRYLATE HAVING A MELTING POINT ABOUT 125%C. AND AMINOR AMOUNT OF BUTYL STEARATE.